1. Field of the Invention
The present invention relates generally to apparatus for pumping fluids. More specifically, the invention provides a simple and compact design for a reciprocating, dual-chamber, compressed air driven pump. The strength of the pump's design facilitates making the pump entirely of corrosion resistant materials.
2. Description of the Background Art
Dual chamber diaphragm pumps are known in the art. Pumps of this type are described in U.S. Pat. Nos. 4,708,601 to Bazan et al, 4,817,503 to Yamada, and 5,108,270 to Kozumplik, Jr. The pumps disclosed in these patents are pumps in which air pressure drives a pair of flexible diaphragms. Each diaphragm draws fluid through an inlet into a pumping chamber and forces the fluid out through an outlet as the diaphragm moves back and forth inside the pump. Such pumps have found widespread use pumping a diverse variety of fluids including water, chemicals, food products and other materials.
Known diaphragm pumps often have complicated designs including small metal fittings and fasteners. These complicated designs hinder disassembly and reassembly of the pumps. This makes routine maintenance and overhaul somewhat difficult. It would be desirable, therefore, to provide an improved pump design that would require less frequent maintenance. It would be further desirable to provide a simpler pump design allowing for convenient disassembly and reassembly to make required maintenance easier to perform.
Some dual chamber diaphragm pumps are adapted to pump corrosive fluids. These fluids would attack and corrode the metal parts commonly used in pumps designed for less demanding applications. In these pumps, some or all of the parts that normally come into contact with the pumped material (the wetted parts) are formed of or coated with chemically inert materials. U.S. Pat. Nos. 4,817,503 and 5,108,270 (mentioned above), as well as U.S. Pat. No. 4,867,653 to Mills et al, describe pumps having some parts formed of corrosion resistant materials.
However, even those pumps whose wetted parts are formed of or coated with corrosion resistant materials almost invariably include some metal parts in other, exterior locations. In many cases metal parts are used as fasteners and fittings to hold the pump bodies and associated tubing together. This is presumably because metal parts are significantly stronger and more easily machined than are corrosion resistant parts, which are typically made of some type of soft (relative to metal) plastic.
Pumps having exposed metal parts only in exterior locations not normally contacted by the pumped fluids are acceptable in many applications. However, such pumps have proven problematic in semiconductor manufacturing applications. These applications are doubly demanding in that extreme purity must be maintained in highly corrosive chemicals including a range of solvents and acids.
No matter how much care is used, it is virtually impossible to completely prevent leakage from a pump in a manufacturing operation. Small quantities of leaked chemicals will eventually contact the exposed fasteners and other metal parts of known pumps. When this occurs, the metal parts corrode and the dissolved corrosion products may leach back into the pump and contaminate the system. In most applications this is not critical--the contaminant quantities are relatively small and ultrapure chemicals are not absolutely essential.
In semiconductor manufacturing, however, even tiny amounts of contamination may be disastrous. Currently, electronic components are fabricated by the millions on single silicon chips and those chips are manufactured in large numbers in automated production runs. Chip failures due to contamination are not typically detected until the individual chips are tested after the manufacturing operation is complete. Under these circumstances, a single source of corroded metal leaking back into the fluid system may cause the loss of many thousands of dollars worth of product. Furthermore, expensive delays occur while the production line is shut down until the source of contamination can be located and the system purged. For these reasons, it would be highly desirable to provide an improved design for a pump in which all parts, inside and out, are made entirely of corrosion resistant materials.